Effects of bariatric surgery on cardiovascular outcomes

Obesity is a major public health problem that is associated with serious comorbidities, including diabetes, dyslipidemia, cancer, and cardiovascular disease (CVD) with premature mortality. Its prevalence has been up trending over the last few decades and is a modern-day pandemic since 2012. Per the American Society for Metabolic and Bariatric Surgery 2023 guidelines, overweight is a body mass index (BMI) of 25 to <30 kg/m² and obesity as a BMI of 30 kg/m².

Over the last decade, the proportion of Australian adults who were overweight or obese has increased from 62.8% in 2011–12 to 65.8% in 2022. This was due to the increase in the proportion of Australian adults categorised as obese, which increased from 27.5% to 31.7% over the same period. Bariatric surgery is increasingly used as a therapeutic option for obesity.

How does obesity contribute to cardiovascular risk?

Obesity is a major contributor to cardiovascular risk factors including hypertension, hyperlipidemia, coronary artery disease (CAD), heart failure (HF), stroke, sleep apnea, and arrhythmias. Its pathogenesis is linked to proinflammatory factors and vessel wall remodelling, among others.

Obesity accelerates atherosclerosis by promoting lipid deposition and atherothrombosis formation. It further activates the cytokines and interleukins causing endothelial dysfunction and vascular remodelling. This translates into cardiovascular disease events including CAD, myocardial infarction, and stroke. Excess visceral adiposity leads to the activation of renin-angiotensin-aldosterone system, cytokine gene expression, and increased systemic circulation of proatherogenic factors. This in turn leads to myocardial fat accumulation, increased stroke volume, cardiac wall remodelling, and fibrosis manifesting as heart failure.

Similar mechanisms lead to left atrial enlargement and fibrosis contributing to arrhythmogenesis.

Management of obesity

Lifestyle modifications and increased physical activity are the initial modalities recommended in the management of obesity. Patients with a BMI of at least 35 or >30 kg/m² with serious obesity-related comorbidities are eligible for bariatric surgery. The commonly performed bariatric surgeries include Sleeve gastrectomy, Roux-en-Y gastric bypass and modified Duodenal Switches. The benefits of bariatric surgery include greater long-term weight loss, reduction of major adverse cardiovascular events (MACE), and cardiovascular mortality.

Obesity poses a high risk for atheroma formation. Bariatric surgery provides a beneficial effect by altering molecular mechanisms involving inflammation. Bariatric surgery decreases the levels of oxidative stress and inflammatory markers. It reduces circulating levels of adhesion molecules and improves endothelium-dependent vasodilatory response. Objectively, several studies have shown that surgery reduces carotid intimal wall thickness in concordance with weight loss. These processes in turn contribute to the risk reduction of atherosclerotic diseases such as CAD, MI, and CVA. Although CAD and MI are atherosclerotic processes, they differ in their pathophysiology and clinical manifestations. CAD is defined as the presence of atherosclerotic plaque within the epicardial coronary arteries. Over time, risk factors potentiate plaque growth. During periods of myocardial oxygen demand, there is endothelial dysfunction causing plaque rupture. This in turn leads to atherothrombosis, vessel occlusion, and myocardial infarction.

Cardiovascular benefits offered by bariatric surgery

Bariatric surgery reduces heart failure risk factors including hypertension, hyperlipidemia, and diabetes. It also directly acts on the myocardium causing changes in the left ventricle (LV) wall and ejection fraction (EF) percentage. Bariatric surgery improves left ventricular systolic dysfunction and resulted in a statistically significant improvement in left ventricle ejection fraction (LVEF). Another study showed a 43% reduction in left ventricular mass with subsequent reduction in left atrial and right ventricular wall diameter and epicardial fat. A meta-analysis done by Cuspidi et al. showed significant changes in LV thickness, improvement in LV diastolic function, and a decrease in left atrial diameter.

Given the significant cardiovascular benefits offered by bariatric surgery, the referral from general practitioners and primary care physicians has been lower. This could be attributed to knowledge gaps, hesitancy, or concerns regarding postoperative care. A recent Canadian survey showed that more than 50% of physician respondents did not feel equipped to counsel the patients on surgical options and only 11.6% of the obese patients were counselled. In a Swedish survey, interestingly, 84% of respondents stated that the patients themselves initiated bariatric surgery referral. Physician’s knowledge showed a positive correlation toward referral and management of postoperative issues. This brings into perspective that education and awareness would lead to better patient sampling, thereby cumulatively improving cardiovascular outcomes.

In conclusion, bariatric surgery shows a statistically significant risk reduction with CAD, MI, HF, CVA, and cardiovascular disease-specific mortality and a non-significant risk reduction of atrial fibrillation.